Screening mammography is a method for detecting signs of breast cancer in otherwise asymptomatic women. The American College of Radiology recommends annual mammography for women over forty. Women undergo an X-ray exam in which X-ray films of the breast are exposed and then developed for later review. A radiologist reads the films and assesses the likelihood of the presence of signs of breast cancer. If a suspicious finding is present, the woman may be invited for additional, more detailed diagnostic X-ray exams, ultrasonic exams, and/or biopsy.
In a typical screening exam in the United States, four X-rays of the breast are obtained. In conventional practice, two mammographic views are obtained for each breast: a cranio-caudal (CC) view is obtained by positioning the X-ray film horizontally under the compressed breast, and a medio-lateral oblique (MLO) view is obtained by positioning the X-ray film in a plane that is approximately orthogonal to the left-right axis. In some situations, more or fewer X-ray views may be obtained. The four views are typically labeled LCC (Left Cranio-Caudal), RCC (Right Cranio-Caudal), LMLO (Left Medio-Lateral Oblique) and RMLO (Right Medio-Lateral Oblique). Knowledge of the laterality (that is, Left/Right side, facing toward the patient) and type of mammographic view (that is, whether the view is a CC or MLO view) is critical for the review process.
It is common in radiological practice to display the different exposures for a patient in a particular format, often referred to as a hanging protocol. Initially devised when film media was used exclusively, the hanging protocol determined the specific spatial arrangement with which the radiologist or technician arranged the films on the light box, according to practitioner preferences. In a conventional hanging protocol for screening mammography, the LCC, RCC, LMLO, and RMLO views are typically displayed in mirrored fashion, such that the thorax edges of both breasts are centered, with the left breast image displayed on the right and the right breast image displayed on the left. However, both breasts images are acquired in a similar manner. It is, in general, not known which image corresponds to the left or the right breast; one image must be flipped before it can be positioned adjacent to the other image. In conventional screen-film imaging, X-ray-markers, for example comprised of opaque lead letters, are radiographed simultaneously (appropriately labeled RCC, LCC, RMLO and LMLO) with the breast tissue. As can be expected, not all films are correctly labeled or oriented properly for viewing, due to technician inexperience or error.
In order to suit practitioner expectations and to allow a smooth transition from film-based to digital radiography, the practice of using X-ray markers still applies for mammography imaging using images scanned from film or computed radiography (CR) cassettes. In place of the conventional light box, high resolution monitors can now be used to display patient exposures as digital images. The same hanging protocol can still be used by the practitioner for display of mammography images.
FIG. 1 shows a typical hanging protocol arrangement that is used. A display 10 has an RMLO image 20, an LMLO image 30, an RCC image 40, and an LCC image 50 arranged as shown. Each image has a corresponding marker 12, placed by the technician nearest the axilla of the patient prior to imaging.
It is desired that the mammography images, once obtained digitally, be displayed in the proper orientation and order in the hanging protocol. In order for this to happen, each image needs to be properly identified as to its type (MLO or CC) and side, or laterality (R or L).
U.S. Pat. No. 5,917,929 (Marshall et al.) entitled “User Interface for Computer Aided Diagnosis System” describes an operator interface panel that accepts operator commands on films for scanning and their proper identification and orientation. While such an approach may be workable for scanned films, however, this type of method requires operator interaction and is subject to operator error. It can be appreciated that automated solutions for detection of type and laterality of digital mammography images would be preferable to those requiring an operator.
There have been some attempts to solve this problem using image analysis techniques. Some examples are provided.
U.S. Publication No. 2004/0161164 (Dewaele) entitled “Method of Detecting the Orientation of an Object in an Image” describes orientation detection using mathematical moments of various axes or landmarks for shape detection.
PCT Application No. WO 02/45437 (Hartman et al.) entitled “Method and System for Automatic Identification and Orientation of Medical Images” describes a method using a set of templates for optical character recognition and other techniques for determining image orientation automatically.
PCT Application No. WO 05/052849 (Bamberger) entitled “Method for Computerized Analysis in Mammography” describes a workstation and method for identifying when an image from film has been inadvertently flipped with the incorrect orientation or rotation.
While these examples may be directed to image orientation, there is room for improvement, particularly with respect to noise effects, handling of operator error, and overall robustness. Thus, there is a need for a capable and robust solution for determining image type and laterality for digital mammography images.